The present invention relates to a sintered body of aluminum nitride and a process for preparing the same, more particularly to a sintered body of aluminum nitride which is dense and excellent in thermal conductivity and a process for preparing the same.
Since aluminum nitride (AlN) deteriorates little in strength going from room temperature to a high temperature, and is exellent in chemical resistance, it is used on one hand as a heat-resistant material, and on the other hand is considered to be promising as a material for heat dissipating substrates of semiconductor devices through the utilization of its properties of high thermal conductivity and good electrical insulation. AlN having the above-described properties usually has no melting point and decomposes at a high temperature of not lower than 2200.degree. C., and therefore, it is used in the form of a sintered body except for the use as thin films.
Said AlN sintered body is usually prepared by molding and sintering an AlN powder. However, when the AlN powder is used singly, sinterability thereof is not good, and therefore, it is impossible to obtain a sintered body which is dense or has a high density except for the case where the hot pressing method is employed. Therefore, in the case of sintering under atmospheric pressure, it is generally practiced to add an oxide of a rare earth metal or an oxide of an alkaline earth metal as a sintering aids to the AlN powder for the purpose of making sintered body denser.
Such an addition of a sintering aids has certainly improved the density of the sintered body to a considerably degree. However, on the other hand, up to today, the thermal conductivity of such AlN sintered bodies has been lower than that of expected due to the presence of oxygen and other impurities and of boundary area of AlN crystal particles. Namely, there is a problem that theoretical thermal conductivity of AlN is 320 W/m.multidot.k, whereas that of an AlN sintered body is 40 W/m.multidot.k at highest.
Therefore, for the purpose of improving thermal conductivity of AlN sintered bodies, various kinds of attempts have been made. However, no AlN sintered bodies which are satisfactory enough have been obtained.